In a power transmitting apparatus that transmits engine power of a vehicle, such as an automobile, to its wheels, it is necessary not only to transmit the power from the engine to wheels but to enable radial and axial displacements. Moment displacement from the wheels is caused by bounds or turns of a vehicle during running on a rough road. One end of a drive shaft arranged between an engine side and a driving wheel side is connected to a differential gear unit, via a constant velocity universal joint of the sliding type. The other end of the drive shaft is connected to a driving wheel via a wheel bearing apparatus including a constant velocity universal joint of the secured type.
Various types of wheel bearing apparatus, for example as shown in FIG. 5, have been previously proposed. The wheel bearing apparatus 50 comprises a wheel hub 51 where a wheel W and a brake rotor B are mounted. A double row rolling bearing 52 rotatably supports the wheel hub 51. A secured type constant velocity universal joint 53 to transmit power to a drive shaft (not shown) is coupled with the wheel hub 51.
The wheel hub 51 is integrally formed at one end with a wheel mounting flange 54. The wheel mounting flange 54 mounts the wheel W and the brake rotor B. A cylindrical portion 51a axially extends from the wheel mounting flange 54.
The double row rolling bearing 52 is formed by a double row angular contact ball bearing. The bearing includes an outer ring 55 mounted between a knuckle N, forming part of the suspension apparatus and the cylindrical portion 51a of the wheel hub 51. The outer ring inner circumference includes double row outer raceway surfaces 55a. A pair of inner rings 56, 56, including their outer circumferences with inner raceway surfaces 56a, 56a, is arranged opposite to the double row outer raceway surfaces 55a, 55a. The double row balls 58, 58 are rollably contained, via cages 57, between the inner and outer raceway surfaces 55a, 55a and 56a, 56a. 
The constant velocity universal joint 53 includes an outer joint member 61 with a cup shaped mouth portion (not shown), a shoulder 59 that forms a bottom of the mouth portion, and a shaft portion 60 that axially extends from the shoulder 59. The outer joint member 61 is inserted into the wheel hub 51 via a serration in a torque transmittable fashion. The shaft portion 60 is fit into the wheel hub 51 until the shoulder 59 abuts against the inner ring 56 of the double row rolling bearing 52. A securing nut 63 is fastened onto an outer thread 62 formed on one end of the shaft portion 60. A predetermined fastening torque on the nut 63 axially, separably, connects the wheel hub 51 and the outer joint member 61.
It is known that a large torque is transmitted to the wheel W, via a sliding type constant velocity universal joint (not shown), from the engine during a low engine speed range such as in starting of the vehicle. Thus, torsion is created in the drive shaft. As the result, torsion is also created in the inner ring 56 of the double row rolling bearing 52 that supports the driving shaft. When a large torsion force is created in the drive shaft, a so-called “stick-slip sound” is generated due to a sudden slip between abutting surfaces of the outer joint member 61 and the inner ring 56.
To cope with this problem in the prior art wheel bearing apparatus 50, a surface treatment to reduce a frictional resistance is formed on a part abutting against the shoulder 59 of the outer joint member 61. More particularly, as shown in FIGS. 6(a) and 6(b), grease grooves 64 are circumferentially formed on the end faces 56b, 56c of the inner ring 56. These grooves 64 help introduce grease into the interface between mutually adjacent surfaces. Thus, this reduces the frictional resistance. Accordingly, a smooth slippage can be caused therebetween and thus the generation of the stick-slip sound can be suppressed. Reference Patent Document 1: Japanese Laid-open Patent Publication No. 110840/2000.
However, these surface treatments made in plural parts increase the machining steps and complicate the process management. Thus, they prevent a reduction of a manufacturing cost.
Additionally in the prior art wheel bearing apparatus, the securing nut 63 is fastened to the outer thread 62 of the shaft portion 60 of the outer joint member 61. A fastening force (axial force) exceeding a predetermined level is required to adjust and control an amount of pre-pressure of the double row rolling bearing 52. Although it is possible to reduce the frictional resistance at first by grease applied between the abutting interfaces, it is believed that the applied grease would be forced out by the fastening force. Thus, it is difficult to keep the friction reducing effect for a long term.